This invention relates generally to water barriers and, more specifically, to barriers which divide water bodies into separate sections, each with a different water quality or elevation.
Numerous hypersaline lakes exist in a dynamic balance between water inflow and evaporation throughout the arid regions in southwestern United States. When activities by man, or nature, change the rate of water inflow from the surrounding watershed, the dynamic balance in the hypersaline water body shifts. Decreases in water inflow produce lower lake water levels and smaller lake volume. If the lake is closed with no outlet, all the dissolved salt contained in the lake must reside in a smaller water volume. A smaller volume with the same total salt produces a higher salinity. In closed water bodies, a lower or higher water elevation represents a significant change in lake volume, thereby inducing significant changes in salinity levels which can cause considerable environmental nuisance or harm to resident fish, wildlife, and vegetation.
A number of approaches have been used for controlling the water quality and elevation of hypersaline lakes in arid regions. One approach is to control only to elevation. In this approach, large pumps are employed to pump excess water to a different area. This approach was recently effective near the Great Salt Lake in Utah. The Great Salt Lake had risen, due to increased in flow, and threatened to inundate a highway. Installation of large internal combustion engine driven pumps and the construction of a lengthy earthen dike allowed excess water to be pumped to another area, thereby lowering the Great Salt Lake. However, the use of large pumps typically entails prohibitively high capital costs and maintenance expenses.
Another approach is to control both elevation and water quality. In this approach, the hypersaline water body is physically divided into separate sections. One section is dedicated to serving as a salt repository while the other section is stabilized at the desired salinity. Typically the salt repository is located so that water from the surrounding watershed does not enter, or is redirected around, the salt repository. If inflow from the watershed decreases, the salt repository can also stabilize the elevation in the stabilized section by varying the water levels within the salt repository. Traditionally, this approach is accomplished by constructing one of a variety of large earthen dikes. The materials used to build such dikes range from hydraulic fill pumped by floating dredges, to sanitary landfill materials, to carefully graded and compacted soils. However, large earthen dikes have significant disadvantages. Being made of earth, dikes are readily susceptible to wave erosion. To minimize damage from wave erosion, large rocks or other xe2x80x9carmoringxe2x80x9d must be placed on the side of the dike. Also, large earthen dikes require relatively flat side slopes in order to maintain slope stability under water. Most notably, the volume of earth required to make a dike increases geometrically as water depths increase. Generally when water depths exceed 25 feet, the large volume of earth required to construct a stable dike makes the dike prohibitively expensive.
An alternative method of dividing water bodies comprises the use of sheet piling such as narrow interlocking strips of steel plate which extend down into the bottom of the water body. However, steel piling is inappropriate in hypersaline lakes because of excessive corrosion rates. Use of alternative materials such as plastics, does not provide the necessary strength in depths greater than 25 feet. Stainless steel or specially coated steel sheet piles are prohibitively expensive. Finally, the sheet pile, once driven into the lake bottom, is difficult if not impossible to remove and relocate.
Another alternative method is the use of inflatable materials such as those used to create inflatable rubber dams. However, inflatable dams require an expensive permanent fixed foundation. If not provided with a permanent fixed foundation, the inflatable dam undergoes large lateral displacements which frequently rupture the connection between the rubber dams and their associated inflation blowers.
Other alternative methods of dividing water bodies have been proposed. In a September, 1997 report by the United States Department of the Interior, Bureau of Reclamation, entitled xe2x80x9cSalton Sea Barrier Curtain Projectxe2x80x9d by Gerald Martin, for example, there is proposed use of a high density polyethylene dam or curtain. The report suggests that the body of water be separated into an evaporative section and a fresher water section. The report recognizes that minor lateral movement is inconsequential so long as it does not damage the barrier nor allow intermixing. The report also recognizes that an absolutely water tight seal is not necessary. This proposed use of a polyethylene curtain has certain advantages compared to the earthen dike and sheet piling concepts because the floating curtain avoids the expense and effort in maintaining an unnecessarily water tight seal along the entire length of the barrier. However, the disadvantages to the use of a polyethylene curtain are significant. The curtain will not resist even minor wind induced currents within the water body and will move large distances if unrestricted. If weighted sufficiently so that lateral movement is impossible, minor currents will push the curtain down, submerging the suspending floats and allowing water to pass from one section to another. Stronger currents will move the curtain laterally to where surface irregularities will snag or tear the curtain again allowing water to intermix.
Yet another alternative method of dividing water bodies makes use of floating concrete structures. Use of floating concrete structures is well known, and various types of floating docks and breakwaters are presently available and in use. However, the prior art types of floating docks and breakwaters have several inherent problems. For one thing, the materials used in such prior art devices to provide buoyancy in both salt and fresh water have consistently been found wanting because of the harsh marine environment. High salinity causes the relentless deterioration of the exposed components and materials thereof. Examples include: woods of various types, hollow fiberglass structures having a variety of shapes and concrete pontoons filled with foams of various types.
U.S. Pat. No. 3,799,093 to Thompson (1974) discloses a floating prestressed concrete wharf which extends the length of previously built concrete wharfs through the use of steel cables. The concrete wharf is encased in a wire reinforcing mesh which acts as temperature and shrinkage reinforcement. However, over time the thinness of the concrete combined with the permeability of concrete will allow highly saline water to enter and corrode the reinforcing steel leading to failure of the wharf. Moreover, the floating nature of the wharf prevents it from submerging, preventing the device from serving as a barrier to divide a water body into separate sections.
U.S. Pat. No. 5,215,027 to Baxter (1993) discloses a concrete floatation module for use as a floating dock or breakwater. The device recognizes the permeability of concrete and suggests the use of polyolefin fibers. The fibers are impervious to corrosion unlike common metal reinforcing materials. While the improvement suggested by Mr. Baxter greatly enhances longevity, the same floating nature of the module prevents it from dividing a water body.
A submergible breakwater disclosed in U.S. Pat. No. 4,938,629 to Boudrias describes a wharf made of hollow shells in which water can be introduced or withdrawn by an air blower. The units are strung together with a cable system and can be submerged or floated as required. The device uses plastic to ensure air tight chambers in concrete. Under submerged hypersaline conditions, however, the plastic is subject to deterioration and attack from a variety of insects and barnacles. Because the depth of the wharf does not extend down to the bottom of the water body, the device is useless to serve as a barrier to divide a water body into separate sections. Moreover, steel reinforcing within the shells corrodes over time expanding as it oxidizes causing more cracks eventually preventing the breakwater from functioning as described.
Accordingly, there is a need for a method of dividing a body of water into two separate parts which avoids the aforementioned problems in the prior art.
The invention satisfies this need. The invention is a method for segregating a body of water into two distinct parts. The method comprises the steps of: (a) forming a plurality of floatable modules; (b) floating each of the plurality of modules into the body of water; and (c) sinking each of the plurality of modules at individual predetermined locations in the body of water.
The floatable modules are each created by (i) forming a generally horizontal base wall and one or more generally vertical walls and (ii) assembling the generally vertical walls to the base wall in such a manner so as to form a floatable module.
The generally vertical walls of each module are chosen so as to have sufficient height to protrude above the water level of the body of water after the module is sunk at its predetermined location. Each of the plurality of modules is sunk within the body of water such that each module is in close proximation to at least one adjoining module and such that the plurality of modules are aligned in a row that bifurcates a body of water into a first portion and a second portion.
Before or after the modules are sunk at their predetermined locations, each module is sealed to an adjoining module such that the plurality of modules effectively segregates the first portion of the body of water from the second portion.
In a typical embodiment, the floatable modules are largely made from concrete, some or all of the walls of the module being poured and assembled to one another at the shore of the body of water where they can easily be into position at their individual predetermined locations.